UPSC Combined Geo-Scientist, Mains · 2026 · Mains Paper III
Q1(a). Classification of samples by size
Question
A geologist received certain samples as follows: Sample 1: 2.50×10⁻¹ g; Sample 2: 2.40×10⁻³ g; Sample 3: 5.00×10⁻⁵ g; Sample 4: 1.50×10⁻² g; Sample 5: 7.00×10⁻⁵ g; Sample 6: 1.75×10⁻³ g; Sample 7: 0.75×10⁻¹ g. Classify the above samples as per their respective sample size following the sampling protocol for analytical chemist.
Answer in brief
Macro: 1. Semimicro: 4 and 7. Micro: 2 and 6. Ultramicro: 3 and 5.
The full model answer
Worked out step by step, as it should go in the answer booklet. The solution sheet follows it.
| Sample | Mass (g) | Mass | Class |
| 1 | 2.50×10⁻¹ | 250 mg | macro |
| 7 | 7.5×10⁻² | 75 mg | semimicro |
| 4 | 1.50×10⁻² | 15 mg | semimicro |
| 2 | 2.40×10⁻³ | 2.4 mg | micro |
| 6 | 1.75×10⁻³ | 1.75 mg | micro |
| 5 | 7.0×10⁻⁵ | 0.07 mg | ultramicro |
| 3 | 5.0×10⁻⁵ | 0.05 mg | ultramicro |
Coversclassification by sample sizeClassification of samples by size
All parts of Question 1
- 1(a) Classification of samples by size5 marks
- 1(b) Stationary-phase film thickness in gas chromatography5 marks
- 1(c) Percentage of amine from the absorbance of its picrate5 marks
- 1(d) Principle of vapour-generation AAS5 marks
- 1(e) Purge gases in thermogravimetric analysis5 marks
- 1(f) X-ray fluorescence in X-ray diffraction5 marks
- 1(g) Argon in ICP-MS; acids for arsenic5 marks
- 1(h) MnO₂ in pyrolusite by back titration5 marks